Pre-stacked optical films

ABSTRACT

Pre-aligned optical layers are stacked and arranged such that an adhesive layer, which is stacked onto the optical layers, contacts at least the uppermost layer and lowermost layer. The resulting subassemblies can be assembled into an optical display without individual handling of the layers, which reduces installation time and manufacturing costs.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/036,521 filed Jan. 14, 2005.

BACKGROUND

The present invention relates to optical displays. In particular, thepresent invention relates to pre-stacked optical films for assembly intoan optical display.

Optical displays, such as backlit liquid crystal displays (LCDs), areused in a wide variety of applications including mobile telephones,personal digital assistants (PDAs), electronic games, laptop computers,monitors, and television screens. Optical films are stacked within anoptical display in order to enhance brightness and improve displayperformance without sacrificing battery life.

Presently, films used in displays are provided as individual films todisplay manufacturers. The films include tabs that are useful inorienting and positioning the films, and cover sheets to protect thesurfaces of the films. During assembly of a display, the cover sheets ofthe films are removed, and the films are stacked, one by one, into aframe that fits between a backlight assembly and an LCD panel.Double-coated rim tape is placed over the stacked films, which seals theedges of the films. A cover sheet is then placed over the rim tape. Tofinish the display, the cover sheet is removed, and the LCD panel isadhered to the rim tape.

This process is difficult and costly in terms of time and material.Creating tabs on the films increases the amount of waste material thatis produced and increases the width of the bezel, or edge, that mustextend around the perimeter of the display to cover the tab. Because thetabs extend to the edge of the rim tape, a path is created that allowsdebris to enter and settle between the films. Removing cover sheets fromindividual films increases assembly time and the possibility of damagingthe films. In addition, as optical films become thinner and thinner, itbecomes increasingly difficult to handle an individual optical film.Thus, resolving these problems would increase product output byincreasing assembly efficiency and reducing the number of damaged films.

BRIEF SUMMARY

The present invention is an optical subassembly for use in an opticaldisplay that includes a plurality of stacked optical films and anadhesive layer. The adhesive layer contacts the uppermost and lowermostfilms of the stack to hold the stack as a unit, so that the stack can beassembled into an optical display without individual handling of theoptical films of the stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 c are exploded views of representative embodiments ofoptical displays.

FIGS. 2 a and 2 b are top and side views of a first representativeembodiment of an optical film unit.

FIGS. 2 c and 2 d are top views of second and third representativeembodiments of an optical film unit.

FIGS. 3 a and 3 b are top and side views of a fourth representativeembodiment of an optical film unit.

FIG. 3 c is a top view of a fifth representative embodiment of anoptical film unit.

FIGS. 4 a and 4 b are top and side views of a sixth representativeembodiment of an optical film unit.

FIG. 4 c is a top view of a seventh representative embodiment of anoptical film unit.

FIG. 5 is a cross-sectional view of an optical film unit installed in achassis.

FIG. 6 is a cross-sectional view of an optical film package installed ina chassis.

DETAILED DESCRIPTION

FIG. 1 a shows a schematic diagram of optical display 10 a, which is notdrawn to scale. Optical display 10 a includes chassis 12; backlight unit14 with reflector 16, light guide 18, and light source 20; diffuser 22;prismatic films 24 and 26; diffuser 28; reflective polarizer 30;adhesive layer 32; display panel 34; optical film unit 36 (formed byelements 22-32); and optical film package 38 (formed by optical filmunit 36 and light guide 18).

Chassis 12 is typically a plastic frame for supporting components ofoptical display 10. In this embodiment, backlight unit 14 includes oneor more layers of reflector 16, along with light guide 18, and lightsource 20. Light guide 18 may include special features for directinglight and can take the form of a slab as shown or other forms such as awedge.

Light source 20 may be any suitable type of light source such as afluorescent lamp, light emitting diodes, or direct lit. Light from lightsource 20 is directed toward display panel 34 via light guide 18.

Next, diffuser 22 is stacked onto light guide 18. Diffuser 22homogenizes the intensity of the light from light guide 18.

Prismatic films 24 and 26 are stacked onto diffuser 22. Films 24 and 26contain arrays of prisms for directing light toward display panel 34.Relative to each other, films 24 and 26 may be arranged such that theirprism arrays run parallel, or more typically, the prism arrays runnon-parallel. As shown in this embodiment, the prism arrays runperpendicular relative to each other.

Diffuser 28 is stacked onto prismatic film 26. Diffuser 28 is typicallya relatively weak diffuser and, as described in regard to diffuser 22,homogenizes the light intensity so that it is more uniform.

The last film shown stacked is reflective polarizer 30. Reflectivepolarizer 30 may be any of a number of types of reflective polarizersincluding a multi-polymer film, a cholesteric polarizer, or a wire-gridpolarizer. Reflective polarizer 30 recycles light that is in the wrongpolarization state and will not be transmitted as image light.

Typically, reflective polarizer 30 is laminated to the back of panel 34.However, as in the case shown here and in the following embodiments,reflective polarizer 30 may be stacked with the other layers.

The next layer is adhesive layer 32 (in bold). Adhesive layer 32 istypically double-coated rim tape or shading frame, but it may also be anadhesive coating. One surface of adhesive layer 32 is black and contactsdisplay panel 34. The opposite surface is colored white or silver andcontacts a portion of each of the layers underneath it. Light tends toleak around the film layers, and the reflective surface of adhesivelayer 32 recycles the leaked light for redirection. The black surfacereduces a “halo effect” around the optical display, which is a brightline that sometimes forms along its perimeter. Suitable rim tapes thatmay be used include 3M Company's Black and White Double Coated PolyesterTape 4003S, 4003T, 4007, 4037, and 4040 and Black and Silver DoubleCoated Polyester Tape 5173. If desired, 3M Company's Black and WhiteSingle Coated Polyester Tape 4038 and 4039 may also be used.

It should be noted that layers 22 through 30 represent one embodiment.Depending on needs and desires, some of layers 22 through 30 may beomitted, added to, or substituted. For example, a turning film with itsprisms facing either up or down may replace prismatic films 24 and 26,or a Vikuiti BEF-RP 90/24 reflective polarizer with prisms may be added.In addition, each layer becomes progressively smaller, and their edgesor perimeters are serially recessed such that portions of the layerscontact adhesive layer 32, which will be explained in more detail below.

Adhesive layer 32 may contact layers 22 through 30 to form optical filmunit 36. Alternatively, adhesive layer 32 may additionally contact lightguide 18 to form optical film package 38. Optical film unit 36 andoptical film package 38 may be referred to as optical subassemblies.Unit 36 and package 38 are assembled prior to delivery to a manufacturerfor assembly of optical display 10. The layers are pre-aligned, so notabs are needed. Adhesive layer 32 seals the edges of the layers, whichremoves any entry point for debris. However, as will be shown below, itis unnecessary for adhesive layer 32 to completely circumscribe theperimeters of the included layers.

FIG. 1 b is a schematic diagram of optical display 10 b. Display 10 bincludes the same layers as display 10 a but additionally includesadhesive layer 25.

Light guide 18, diffuser 22, and prismatic film 24 become seriallysmaller as previously shown. Adhesive layer 25 is stacked onto prismaticfilm 24 and sized similarly to adhesive layer 32 such that one surfaceof adhesive layer 25 contacts and secures each of layers 18 through 24or 22 through 24. Next, prismatic film 26, diffuser 28, and reflectivepolarizer 30 are stacked. Instead of continuing to decrease in size asin Figure la, however, each layer becomes serially larger. Adhesivelayer 32, which is sized identically to that shown for display 10 a, isthen stacked onto reflective polarizer 30. The remaining surface ofadhesive layer 25 contacts layers 26 through 32.

Adhesive layer 25, unlike adhesive layer 32 is not rim tape but is anytype of suitable double-coated tape. With this embodiment, the layersmay be more secure, and the smallest layer of display 10 b is largerthan the smallest layer of display 10 a. Thus, a larger viewing area isprovided without increasing the overall size of the layers.

FIG. 1 c is a schematic diagram of optical display 10 c. Again, display10 c includes the same layers as display 10 a.

Here, light guide 18 is larger than layers 22 through 30. Layers 22through 30 are the same size, and adhesive layer 32 only contacts aportion of light guide 18 and reflective polarizer 30. The remaininglayers are trapped between light guide 10 and reflective polarizer 30,and the edges of each layer are sealed to prevent debris from entering.

Note that in order to form unit 36, diffuser 22 would be sized largerthan the remaining layers to adhere to adhesive layer 32. As withdisplay 10 b, the smallest layers are larger than the smallest layer ofdisplay 10 a, which provides a larger viewing area without increasingthe films' overall size.

FIGS. 2 a and 2 b are top and side views, respectively, of optical filmunit 36. Unit 36 includes adhesive layer 32 having outer perimeter 32 p′and inner perimeter 32 p″, diffuser 28 having outer perimeter 28 p, andreflective polarizer 30 having outer perimeter 30 p. Recess distancesd1, d2, and d3 are also shown in FIG. 2 a. Only two layers, 28 and 30,are shown for simplicity. However, any number and type of film used inmanaging light for an optical display, such as those described for FIGS.1 a-1 c, may be used.

Diffuser 28 is the bottom layer with reflective polarizer 30 beingstacked on top. As is evident in FIGS. 2 a and 2 b, diffuser 28 islarger than reflective polarizer 30, and the films are arranged suchthat outer perimeter 30 p is recessed by distance dl from outerperimeter 28 p.

In this embodiment, adhesive layer 32 has a frame-type shape and isstacked over diffuser 28 and reflective polarizer 30. Inner perimeter 32p″ is recessed by distance d2 from outer perimeter 30 p, while outerperimeter 32 p′ extends beyond outer perimeter 28 p by distance d3.Thus, a portion of each of diffuser 28 and reflective polarizer 30contacts and adheres to adhesive layer 32. Ideally, a protective coversheet (not shown) is stacked over adhesive layer 32 and under thelowermost layer. The cover sheets are removed prior to attaching panel34 to unit 36 to create a display module. Suitable protective coversheets and their method of attachment are described in Ser. No.10/750,553, filed on Dec. 31, 2003.

Distances d1, d2, and d3 are about 2.0 mm or less or, more typically,about 1.0 mm or less. Distances d1-d3 may not be identical to each otherand may not be uniform along any of the entire perimeters of the layers.

As evident in FIG. 2 b, adhesive 32 must conform to the geometry of thestaggered edges of the layers in order to contact a portion of eachlayer. It is shown exaggerated for purposes of illustration. The filmsare thin, and adhesive layer 32 would not normally require such aconformation.

Unit 36 is much easier to handle than each film individually and issealed, which prevents debris from accumulating between films. The filmshave no tabs, because they are pre-aligned and the manufacturer needonly align outer perimeter 32 p′ within a chassis in order to correctlyposition optical film unit 36. In addition, tab-less films result innarrower borders around the viewing area. This allows manufacturers toincrease the size of the viewing area without increasing the overallsize of the device. This is especially significant for small devicessuch as mobile phones and PDAs.

FIG. 2 c is a top view of optical unit 36 a, which is similar to unit 36but includes holes 40 and slots 42 within reflective polarizer 30. Holes40 may have any of a number of types of shapes such as circles orsquares. Although two are shown here, there may be one or more along anyportion of or all of outer perimeter 30 p. Holes 40 should measure lessthan about 2 mm across, but will typically measure about 0.5 mm to about1.0 mm.

Slot 42 is also shown. Slot 42 may have any of a number of elongatedshapes such as a rectangle or oval. There may be one or more of slot 42along outer perimeter 30 p and can be in any combination with holes 40.Slot 42 may have any length, but its width should be less than 2 mm,typically between about 0.5 mm and 1.0 mm.

Holes 40 and slot 42 should be about 0.50 mm or less from outerperimeter 30 p and inner perimeter 32 p″. Typically, additional layerssized the same as reflective polarizer 30 and also having holes 40and/or slot 42 would be included. Only the lowermost layer is sizedlarger and does not include holes 40 or slot 42. Thus, each of thelayers is secured and sealed from entry of any debris.

The use of slot 42 secures the layers as a unit, but also allows somemovement of the layers in the direction of the width of slot 42. Thus,this embodiment may better tolerate any adjustments between the layersshould it be necessary.

FIG. 2 d is a top view of optical unit 36 b, which is also similar tounit 36 but includes notches 30 n on reflective polarizer 30. Here,outer perimeter 30 p extends out to outer perimeter 28 p except wherenotches 30 n are recessed by distance d1. There may be any numbernotches 30 n having any size along outer perimeter 30 p. Notches 30 nmay have any type of shape such as, for example, a triangular shape, andit is not necessary that perimeter 30 p extend out to outer perimeter 28p.

FIGS. 3 a and 3 b are top and side views, respectively, of optical filmunit 36 c. Unit 36 c includes diffuser 28 having edges 28 a and 28 b,reflective polarizer 30 having edges 30 a and 30 b, adhesive layer 32′having outer edge 32 ′o and inner edge 32 ′i, and adhesive layer 32″having outer edge 32 ″o and inner edge 32 ″i. Recessed distances d1, d2,and d3 are also included. Edge 28 a is opposite edge 28 b, and likewise,edge 30 a is opposite edge 30 b.

Unlike the embodiment of unit 36, the full perimeter of the films andadhesive layer are not staggered relative to one another. In addition,the adhesive layer is in the form of only a portion of a frame-typeshape. Edges 30 a and 30 b are recessed from edges 28 a and 28 b,respectively, by distance d1. Edges 32 ′i and 32 ″i are recessed fromedges 30 a and 30 b, respectively, by distance d2. Edges 32 ′o and 32 ″oextend beyond edges 28 a and 28 b, respectively, by distance d3. Again,distances d1-d3 need not be identical to each other or uniform alongeach edge.

Though unit 36 c has two remaining edges of each layer that are notstaggered and have no adhesive layer, unit 36 c is still assembled andinstalled as a unit. The advantage is that a device into which it isinstalled will require only a minimal bezel to cover the two remainingedges. Thus, unit 36 c provides a maximum viewing area in one dimension.

Any two edges along the perimeters of diffuser 28 and reflectivepolarizer 30 may be staggered and secured with adhesive layers 32′ and32″. In addition, it may be desirable to stagger and secure a third edgeof unit 36 c.

FIG. 3 c is a top view of optical unit 36 d, which is similar to unit 36c but includes adhesive layer 32 and shows outer perimeter 30 p. Here,adhesive layer 32 has a frame-type shape that extends around the entireperimeter of the layers. Edges 28 a and 30 a are staggered relative toeach other, and edges 28 b and 30 b are also staggered relative to eachother as shown in unit 36 c. The remaining two edges of films 28 and 30are not staggered, and inner perimeter 32 p″ is recessed from outerperimeter 30 p by distance d2. The remaining edges of diffuser 28 do notcontact adhesive layer 32.

Unit 36 d also maximizes the viewing area in one dimension. In addition,additional layers may be added between films 28 and 30 that are sizedthe same as reflective polarizer 30 giving a configuration similar tothat shown in FIG. 1 c.

FIGS. 4 a and 4 b are top and side views of optical film unit 36 e. Unit36 e includes diffuser 28 having edge 28 a, reflective polarizer 30having edge 30 b, and adhesive layer 32′ having outer edge 32 ′o andinner edge 32 ′i. Again, recessed distances d1, d2, and d3 are shown.

In this embodiment, only one edge is secured. Diffuser 28 is at thebottom of the stack followed by reflective polarizer 30 and thenadhesive layer 32′. Edge 30 a is recessed from edge 28 a by distance d1.Edge 32 ′i is recessed from edge 30 a by distance d2. Edge 32 ′o extendsbeyond edge 28 a by distance d3. The advantages of unit 36 e are thatunit 36 e is still handled as a unit instead of as single films, but ifnecessary, the films may be fanned out in order to remove any debristhat may settle between the films.

FIG. 4 c is a top view of optical unit 36 f, which is similar to unit 36e but includes adhesive layer 32 and outer perimeter 30 p. Edges 28 aand 30 a are staggered relative to each other. The remaining edges arenot staggered, and inner perimeter 32 p″ is recessed from outerperimeter 30 p by distance d2. The remaining edges of diffuser 28 do notcontact adhesive layer 32.

Additional layers may also be added to any of the previous embodiments.For example, additional film layers and an additional adhesive layersuch as shown in FIG. 1 b may be combined with the embodiment of unit 36f. In this example, only one edge of each layer would be seriallystaggered. In all embodiments, recessed distances d1-d3 are typically2.0 mm, but preferably 1.0 mm or less.

The films and adhesive layers shown in these embodiments can have anygeometric shape, including circular and oval shapes. In addition, theseembodiments also apply to optical film package 38 (FIGS. 1 a-1 c) simplyby adding a light guide to the bottom of the plurality of stacked films.

FIG. 5 shows optical film unit 36 e as assembled into chassis 12, whichare not drawn to scale. FIG. 5 includes chassis 12, reflector 16, lightguide 18, and unit 36 c with adhesive layer 32′ and plurality of stackedoptical films 44. Films 44 are shown having three films, but it mayinclude any number of films such as those shown in and described inreference to FIGS. 1 a-1 c.

Light guide 18 is attached to chassis 12. Unit 36 e is installed bypositioning the edge of adhesive layer 32′ within chassis 12. Adhesivelayer 32′ adheres to chassis 12 to secure unit 36 e. As shown in FIG. 5,adhesive layer 32′ must conform to the geometry of the staggered layersand attachment to chassis 12.

FIG. 6 shows optical film package 38 a as assembled into chassis 12 a,which are not drawn to scale. FIG. 6 includes chassis 12 a, reflector16, and package 38 a with light guide 18 a, adhesive layer 32′, andplurality of stacked optical films 44.

In this embodiment, package 38 a is installed by positioning adhesivelayer 32′ within chassis 12 a. Chassis 12 and chassis 12 a and lightguides 18 and 18 a are slightly different to accommodate installation ofan optical film unit or an optical film package, respectively. Again,adhesive layer 32′ conforms to the geometry needed to contact portionsof light guide 18 a, optical films 44, and chassis 12 a.

The present invention provides a more efficient and less costly productfor installation into an optical display. The optical layers may bepre-aligned and stacked in bulk by means of a continuous web, which ismore efficient and effective than stacking each layer individually as ispresently done. Because the layers are not individually stacked, they nolonger require peripheral tabs for positioning and orienting norprotective cover sheets. In addition, the films may be sealed to preventany debris from entering between the layers.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. An optical subassembly for use in an optical display, the opticalsubassembly comprising: a plurality of stacked optical films having anuppermost film and a lowermost film, each of the uppermost and lowermostfilms having at least first and second edges; and first and secondadhesive layers contacting the uppermost and lowermost films of thestack on the first and second edges of the uppermost and lowermost filmsto hold the stack together as a unit, so that the stack can be assembledinto an optical display without individual handling of the optical filmsof the stack.
 2. The optical subassembly of claim 1 and furthercomprising: at least one intermediate film between the uppermost andlowermost films of the stack.
 3. The optical subassembly of claim 2wherein the two edges of the optical films are staggered.
 4. The opticalsubassembly of claim 2 wherein the optical films are configured suchthat each optical film contacts the first and second adhesive layers. 5.The optical subassembly of claim 1 wherein third edges of the opticalfilms are staggered.
 6. The optical subassembly of claim 1 wherein atleast one optical film includes voids to allow the first adhesive layerto contact the lowermost film.
 7. The optical subassembly of claim 1further comprising a protective cover sheet.
 8. The optical subassemblyof claim 2 wherein the at least one intermediate film between theuppermost and lowermost films of the stack is selected from the groupconsisting of a turning film, a prismatic film, a reflective polarizer,a diffuser, and combinations of any of them.
 9. The optical subassemblyof claim 2 wherein the at least one intermediate film between theuppermost and lowermost films of the stack is two prismatic films. 10.The optical subassembly of claim 1 wherein the each of the first andsecond adhesive layers have two major sides and have an adhesive on eachof the two major sides.
 11. The optical subassembly of claim 1 whereinthe each of the first and second adhesive layers have two major sides,wherein one of the major sides is black and the other major side iswhite or silver.
 12. The optical subassembly of claim 1 wherein thefirst and second edges have a length and the first and second adhesivelayers contact the length of the first and second edges.
 13. The opticalsubassembly of claim 1 wherein each of the uppermost and lowermost filmshas four edges and first, second, third, and fourth adhesive layerscontacting the uppermost and lowermost films of the stack on the fouredges of the uppermost and lowermost films.
 14. The optical assembly ofclaim 13 wherein the first, second, third, and fourth adhesive layersare a unitary adhesive layer having a shape of a frame.
 15. The opticalsubassembly of claim 1 and further comprising: a light guide stackedunder the lowermost film which is configured to allow the first andsecond adhesive layers to contact the light guide.
 16. An optical filmpackage comprising in combination: a light guide; and an opticalsubassembly of claim
 1. 17. The optical film package of claim 16 whereinthe adhesive layer has a portion of a frame-type shape.
 18. An opticaldisplay comprising in combination: a backlight unit; a display panelunit; and an optical film subassembly of claim 1 positioned between thebacklight unit and the display panel unit.
 19. The optical display ofclaim 18 wherein the backlight unit further comprises: a light guide;and at least one light source.
 20. The optical display of claim 18wherein the adhesive layers secure the optical film subassembly to thedisplay panel unit.